Green Tea and Kidney Stones

Green tea has a long list of benefits, and one area where it could be beneficial is in relation to kidney stones. This may seem controversial to some people – tea contains oxalic acid, and with oxalic acid forming a major part of most kidney stones the drinking of tea has often been said to increase the likelihood of developing them. But, several studies are finding different results when it comes to green tea, and it seems that oxalic acid content isn’t everything; drinking green tea could actually prevent the formation of the dreaded stones.

A lot of scientific studies are confirming that green tea can have a beneficial effect in relation to kidney stones, with one such study, published in 1998 in the Annals of Internal Medicine, finding that women who drank green tea had a significantly lower risk of developing kidney stones than those who didn’t. The study was conducted over a period of 8 years and included 81,093 women aged between 40 and 86, and they found that for each cup of green tea that was consumed the likelihood of developing kidney stones dropped by 8%.

A similar study, this time conducted on rats, took place in 2005. Researchers at the Nagoya City University Graduate School of Medical Studies found that rats that drank green tea were less likely to develop such stones in the urinary tract, and a similar study in 2006 confirmed these findings. The study, conducted at the Seoul National University, found that the antioxidants in green tea could prevent the formation of urinary stones, thus offering hope for people who suffer from them.

But why should green tea have such an effect? One theory, as already mentioned, is the high antioxidant levels in green tea. These antioxidants can have a marked effect on a lot of processes in the human body, but researchers at Sichuan University in Chengdu, China, took this one step further.

In 2009, Xudong Li and colleagues published a study in CrystEngComm that looked at the specific effects that green tea had on calcium oxalate crystallation, the primary way that kidney stones are formed. They found that as the amount of green tea applied increased the crystals formed became flatter, and the smaller and flatter the crystals are the less likely they are to create stable kidney stones and the easier they are to break up. The researchers argue that it’s the compounds found in green tea, specifically compounds known as phenols, that stop kidney stones from forming – the phenols in green tea attach themselves to calcium oxalate crystals, making them a different shape and as such less likely to clump together to form stones.

This offers the first clear scientific evidence of why green tea can have such a marked effect on the incidence of kidney stones, and studies are continuing to be conducted to look even closer at the benefits of the tea. So, if you’re susceptible to kidney stones, or even if you’re not and you just want to have extra protection, then make sure to add green tea into your daily diet to see if it makes a difference.

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